For decades, the Weather Service marked the monsoon with a technical measurement. The monsoon began when the average daily dew point was 55 degrees or greater for three consecutive days. The season began on the first of those days.
Typically, that meant the first week of July.
But in 2008, the Weather Service decided to keep things simple. The Arizona monsoon season, it says, starts June 15 and ends Sept. 30.
The idea was that people were getting too hung up on figuring out when the season started and were not paying attention to the storms. Those can be quite dangerous, with high winds, lightning and some flash flooding. So, the Weather Service put an end to all that and gave dates to the season. "It's basically summer plus a week or two on either side," said Doug Green of the Weather Service.
Monsoon facts
Recent start dates
2000: June 17
2001: June 21
2002: July 9
2003: July 18
2004: July 12
2005: July 18
2006: July 2
2007: July 19
2008: July 3*
2009: June 30*
Average rainfall by month
June: .09 inch
July: .99 inch
Aug.: .94 inch
Sept.: .75 inch
*Unofficial.
Source: National Weather Service
